The design and development of thermal insulating materials, is an extensive art. Many systems have been developed employing, as the major insulating materials, various fibrous and powder products. There have also been a variety of ways for utilizing these materials, including the use of evacuated shells and bags, compression of the insulating materials, and varying orientations of the insulating materials.
In U.S. Pat. No. 4,636,415 entitled "Precipitated Silica Insulation," assigned to the same asignee as the present invention, the use of precipitated silica as an insulator to achieve good insulating properties at relatively low cost has been described. The precipitated silica, in accordance with that application, is dried at a temperature sufficient to drive off the surface water, is then compressed, placed in a gas and water tight envelope which is evacuated, and the gas and water tight pouch then sealed.
Additionally, in U.S. Pat. No. 4,681,788 entitled "Insulation Formed of Precipitated Silica and Fly Ash," assigned to the same assignee as the present invention, the use of such precipitated silica in combination with fly ash and fly ask-like materials is described. This combination of materials is employed in the same manner as the precipitated silica, alone, i.e., it is compressed, placed in a gas and water tight envelope which is evacuated, and the gas and water tight envelope then sealed.
While each of the systems just described forms a more than adequate insulating material, it would be extremely desirable to form insulation having the same ostensible structure, but where evacuation and maintenance of a vacuum at the extremely low levels required would not be necessary. By this invention, a system has been developed using the materials described in the referenced copending applications, as well as other particulate materials, but with added components, providing the same isulating properties without the necessity for the extremely low vacuums.